I'm not sure about what script to use but I recall I was using SpeedFu (along with FuBar) at some point, to display my current moving speed onto FuBar. If reading code doesn't bother you I guess the script command(s) to get such a result are in this little addon (or you can use SpeedFu just for checking and then ditch it).

Changing aspects will always break a channel if it's already started. However, you can have some decent luck with:

/cast [nochanneling] !Aspect of the Hawk
/cast Serpent Sting (or whatever)

Since aspects are on their own 1s cooldown separate from the GCD, you can change before starting a channel without any penalty.

Whats a macro i can use to cast on my self while holding my current target. I was told to use
/target [self]
/cast SkillNameHere
/target [lasttarget]

The target [self] and the target [lasttarget] dont seem to work. What else can i try?

/cast [target=player] spellname

[target=player] will always target your self, the player, it's not a conditional.

Is it possible to macro a virtual cooldown to a spell? For example, if I press it, it'll cast Demo Roar, but subsequent presses will never produce a result until however-many seconds later.

Not perfectly certain it will work, but in principle you should be able to use a cast sequence with a reset and fill up the rest of the casts with "dummy" calls. I've used similar macros before, but there might have been changes since then to the macro language.

So use an ability that either is impossible to cast in the form you're in (but make sure that you don't switch form automatically), use an ability that is unusable in combat or use an ability that has a long cooldown (that you have already used).

For druids and demo roar something like this ought to work (assuming that the use of Wrath won't shift you to caster shape):

/castsequence reset=30 Demoralizing roar, Wrath

When pressed for the second time this will do nothing (but should give an error, which can be turned off in the macro by adding some stuff) and will continue to do nothing at subsequent keystrokes until 30 seconds have passed and demo roar has to be applied again.

The macro doesn't quite work:

If I press it once at t-0, it casts Demo Roar. If I never press the macro again, it will return to Demo Roar at t+30.

If I press it once at t-0, it casts Demo Roar. If I press the macro again at t+10, nothing is cast, but this apparently causes the reset to "reset" its counting, such that it would only return to Demo Roar at t+40.

That is correct. The reset= function means "this is how long to wait with no function before i reset myself, if an action is taken the timer starts again."

The only way i can think of to do what you want would be to put a
#showtooltip
/castsequence reset=30 Demoralizing roar
macro on your bar, using the question mark icon, and use it as a reminder for when you need to use the ability.

When the timer you put is in done, the ability will show on the button, otherwise it won't be anything (or you may need to add another, random ability after Demo roar in the sequence, in which case it'll show that 'till the timer is up). I'm relatively sure there isn't a way to hard-wire a button to not do anything depending on a timer, at least not with the in-game macro system.

Blizzard has intentionally made it impossible to choose a spell based on buffs in combat. And if you find a way around it, they'll try to prevent it.

If your problem is that you press the button 3 or four times in the space of a second or two, you could use

/castsequence reset=1 !Aspect of the Hawk, null

which would do nothing unless you haven't hit the button in a second. You could also add the [nochanneling] but if you hit the button while channeling by mistake, you couldn't hit it again until a second had elapsed. I THINK the following would do what you want, but I can't test it here.

This will NOT help if your problem is that you press the button when you didn't need to, for example 5 seconds after you turned on the aspect in the first place. But it will help if you start rapidly spamming the keys, and should cast the spell the moment channeling ends if you start spamming the button while channeling. Once again, I haven't tested it, I just saw no one had quite answered the question and wanted to help.

From what I've seen its basically calling the API command, waiting for an event and parsing the returned data.
QueryQuestsCompleted() - Call this.
QUEST_QUERY_COMPLETE - Have it registered under events and wait for it to be triggered.
GetQuestsCompleted([table]) - Then parse this under a LUA Table.

Mind you, there isn't a whole lot of documentation on it right now.